1. Field of the Invention
This invention relates to a rotational speed controller such as an endless rotation damper and the like.
2. Description of Related Art
A roller blind mounted on a window, for example, incorporates a torsion spring having a turning force acting in the winding-up direction of the roller blind. When winding the roller blind down, a rotation braking mechanism of the torsion spring prevents the blind from being wound up. On the other hand, when winding up the roller blind, the rotation braking mechanism is disengaged to allow the torsion spring to automatically wind up the blind.
When the roller blind is wound up as described above, a winding force is accelerated and therefore the roller blind may be rolled up quickly and sharply. If the blind is rolled up quickly in this way, a stopper provided at the lower hem of the blind hits a winding shaft with a loud noise, and in some cases, the stopper itself or the winding shaft may be broken.
Therefore, a rotational speed controller such as an endless rotation damper or the like is used for slowly rolling up the roller blind. The conventional endless rotation damper is designed as follows.
A shaft is rotatably supported in a casing, and fitted with a rotor rotating together with the shaft in one piece. The casing fitted with the shaft and the rotor is filled with a viscous fluid, and sealed with a cap. Inside the casing fitted with the shaft and the rotor and sealed with the cap, a fixed clearance is formed between the outer periphery of the rotor and the inner periphery of the casing and filled with the viscous fluid.
In the above construction, upon rotation of the shaft, the rotor is rotated in relation to the casing. Upon the rotation of the rotor in relation to the casing, the viscous substance provided between the rotor and the casing has shearing resistance. The shearing resistance provides braking torque on the rotating shaft to prevent the roller blind from being rolled up quickly.
In the above conventional endless rotation damper, if a high braking torque is required, there is no choice but to increase the rotational speed of the shaft. This is because a magnitude of the shearing resistance generated between the rotor and the casing is determined by the rotational speed of the shaft, in which the higher the rotational speed of the shaft is, the higher the shearing resistance which is generated between the rotor and the casing. Accordingly, when a higher braking torque is required, the rotational speed of the shaft is increased to increase the shearing resistance.
However, in the case of the above endless rotation damper, a rotational speed of the shaft is determined in accordance with the use thereof. In the endless rotation damper designed as described above it is impossible to increase its braking torque.
Therefore, one known endless rotation damper which is capable of developing a high braking torque without increasing the rotational speed of the shaft is described in Japanese Patent Laid-open No. 2-292480, of which the device is shown in FIG. 7 attached to the present application.
As shown in FIG. 7, a shaft 2 is held rotatably in a case 1. Inside the case 1, a plurality of stationary disks 4 is mounted in a direction orthogonal to the shaft 2. On the shaft 2 a plurality of movable disks 3 is mounted in a direction orthogonal to the shaft 2.
Each of the movable disks 3 is disposed between two stationary disks 4.
After the shaft 2 and the movable disks 3 are assembled in the case 1 provided with the stationary disks 4 as described above, the case 1 is filled with a viscous fluid 5 and sealed with a cap. The viscous fluid 5 is interposed between each stationary disk 4 and each movable disk 3.
In the above construction, upon rotation of the shaft 2, the movable disks 3 mounted on the shaft 2 are rotated in relation to the stationary disks 4. At this point, shearing resistance is generated between each movable disk 4 and each stationary disk 3. That is, the number of points at which the shearing resistance is generated is increased to increase the shearing resistance in the entire damper, thus providing a high braking torque.
In order to obtain a higher braking torque in the above conventional damper, it is needed to increase the number of stationary disks 4 or movable disks 3 or to increase a diameter of each disk. However, the length in the shaft direction is inevitably increased if the number of disks is increased, and likewise the size in the radial direction if the diameter of each disk is increased, resulting in an increase in size of the entire damper.
Therefore, there is a limit to the increase in the number of disks and the diameter of each disk. This limit leads to the problem of a limit to the production of a high braking torque.
Another problem is that the variation in the braking torque between the dampers is increased as the number of stationary disks 4 and movable disks 3 is increased.
For example, the more the number of stationary disks and, movable disks is increased, the more easily a dimension error in assembling is produced and the more easily a variation in spacing between the disks is produced. If the spacing between the disks varies, the shearing resistance which is dependent upon the spacing also varies, which creates another problem of there being a different braking torque even between dampers of the same specifications. Further, there is another problem that it is difficult to obtain the required torque assumed in the design process.
It is a first object of the present invention to provide a rotational speed controller which is capable of increasing baking torque without a corresponding increasing in size. It is a second object of the present invention to provide a rotational speed controller which is capable of easily outputting braking torque assumed in a design process, and minimizing variations in the braking torque.
The present invention provides a rotational speed controller according to a first feature which comprises a casing filled with a viscous fluid; a shaft rotating relatively to the casing; a first rotor incorporated in the casing; a second rotor rotating relatively to the first rotor with a gap between itself and the first rotor; a cap for hermetically sealing the casing; a first rotation mechanism for rotating the first rotor; and a second rotation mechanism for rotating the second rotor, shearing resistance being generated between the first rotor and the second rotor.
A second feature is that a gap is maintained between the inner periphery of the casing and the outer periphery of the first rotor, and shearing resistance is generated between the inner periphery of the casing and the outer periphery of the first rotor.
A third feature is that the first rotor and the second rotor are rotated in the opposite directions to each other.
A fourth feature is that the first rotor and the second rotor are rotated relatively by a planetary gear mechanism.
A fifth feature is that the first rotor and the second rotor are driven by a same driving source.
A sixth feature is that the first rotor and the second rotor are driven individually by separate driving sources.
According to the present invention, the rotational speed controller comprises: a casing filled with a viscous fluid; a shaft rotating relatively to the casing; a first rotor incorporated in the casing; a second rotor rotating relatively to the first rotor with a gap between itself and the first rotor; a cap for hermetically sealing the casing; a first rotation mechanism for rotating the first rotor; and a second rotation mechanism for rotating the second rotor, and is designed so as to generate shearing resistance between the first rotor and the second rotor. With the above design, the shearing resistance is generated on both the first rotor and the second rotor. The shearing resistance generated on both the first rotor and the second rotor is higher than that generated on either one of the rotors.
Because of the design capable of generating a high shearing resistance between the first rotor and the second rotor, there is no need to provide extra points for generating shearing resistance. Accordingly, it is possible to reduce the number of assembled members, and thereby decrease the amount of assembly error caused when the members are assembled. In turn, the decrease in the assembly error leads to a decrease in variations in the shearing resistance which are caused by the assembly error. The decrease in variations in the shearing resistance as described above makes it possible to reliably provide torque assumed in the design process.
In particular, according to the second feature, a gap is maintained between the inner periphery of the casing and the outer periphery of the first rotor, and shearing resistance is generated between the inner periphery of the casing and the outer periphery of the first rotor. Hence, the shearing resistance generated between the first rotor and the second rotor is added to by the shearing resistance generated between the first rotor and the casing, to act upon the shaft. Accordingly, a further higher shearing resistance is provided.
In particular, according to the third feature, the first rotor and the second rotor are rotated in the opposite directions to each other, so that the sharing resistance generated on each of the first rotor and the second rotor is further increased. In addition, the rotation of the first rotor and the second rotor in the opposite directions to each other provides braking torque for braking the rotation of the shaft.
In particular, according to the fourth feature, the first rotor and the second rotor are relatively rotated by a planetary gear mechanism. Hence, the first rotor and the second rotor are rotated in opposite directions at low cost and with high accuracy. In addition, the braking torque is adjusted by changing the gear ratio of the planetary gear mechanism, and a rotational speed controller with a high speed dependence is provided. When the gear ratio of the planetary gear mechanism is changed in this way, it is possible to provide braking torque in accordance with the use.